Wismar, seaport and manufacturing city, Mecklenburg, Germany, was the scene of some Anabaptist activity and conferences. On 11 April 1535 at a conference of evangelical theologians at which action against Anabaptists was taken, Wismar was represented. This does not prove that there were Anabaptists in this city at this early date. When Menno Simons lived at Wismar during the winter of 1553-1554 there was a considerable group of Anabaptists there. On 21 December 1553, the refugee congregation led by the Reformed preacher á Lasco arrived there from London. Menno and Martin Micron, the latter representing this refugee congregation, held a debate in Wismar on basic Christian doctrines. On 6 February 1554, another discussion, particularly on the incarnation of Christ, took place, which was continued on 15 February. Menno and Micron continued their discussion in several published writings.

Three days after the meeting, Menno was informed by "the city council that Anabaptists were not to be tolerated in the city because the discussions had become known. Menno accused Micron of reporting the Anabaptists to the city council. Particularly the Lutheran ministers of Wismar, Smedenstede and Vincentius, aroused the city council against the Anabaptists which decreed that the latter had to leave the city by 11 November 1554. It was probably at this time that Menno left Wismar to find a new shelter at Wüstenfelde .

A significant meeting of Anabaptist elders in Wismar in 1554 resulted in the Wismar Resolutions, which played a very significant role in the later development of Anabaptism in the Netherlands and northwest Germany. It is likely that Gillis van Aken was received into the fellowship here after having been excommunicated.